1. Field of the Invention
This invention relates to a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte, and a method for fabricating a non-aqueous electrolyte secondary battery.
2. Description of Related Art
Compared with other secondary batteries such as lead-acid batteries or alkaline batteries, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have a high energy density and therefore are widely used as power supplies of portable devices such as mobile phones. In recent years, much study and development have been carried out for use of a non-aqueous electrolyte secondary battery as a power supply for a movable object such as an electric vehicle.
Though the non-aqueous electrolyte secondary battery like lithium ion secondary battery has high energy density, its battery performance is lowered, for example, the discharge capacity is lowered or the internal resistance is increased, due to repeated charge/discharge or long-term storage. The lowering of battery performance is mainly caused by the reaction between the electrode plate and the non-aqueous electrolyte. To inhibit the lowering of battery performance, it has been studied to add various additives to the non-aqueous electrolyte. For example, Japanese Patent Publication No. 1999-162511 discloses using a sulfate ester as an additive of a non-aqueous electrolyte.
As a power supply for a movable object such as an electric vehicle or a hybrid-electric vehicle, the battery is used under severe temperature conditions. For example, when the movable object is used in a cold region or in winter, the temperature of the battery may be below zero. On the other hand, when being used in summer, the battery may have a temperature up to 60° C. due to its carrying position. Therefore, the battery carried on a movable object needs to exert its performance in a wide temperature range. However, it is found that a battery charged/discharged repeatedly in a high-temperature circumstance or stored for long time in a high-temperature circumstance is increased in the internal resistance and lowered in the power performance. Particularly, compared with the internal resistance at a normal temperature, the internal resistance at a low temperature is increased significantly. Therefore, when the battery is used in a low-temperature circumstance after being used in a high-temperature circumstance, there is a problem that a sufficient power performance cannot be ensured.